Mayer, 35, was joined by a male friend and didn't appear to interact with Aniston, 44, but "saw her when he came in," a source tells PEOPLE.

But what could have been an awkward run-in was a fun night with friends for Aniston.

"There was a bottle of wine on Jen's table. Looked like a cute dinner with friends. They are all having fun and Jen and Justin look very sweet together," the source adds.

Aniston and Mayer's romance began in 2008 but called the couple called it quits that August. They soon reconciled and attended the Vanity Fair Oscars afterparty together, taking their relationship public. But after a year of on-and-off dating, they split again – for good – that March.

Last August, Aniston and Theroux, 41, got engaged after more than a year of dating. But the actress has stayed mum about her impending nuptials. Even Aniston's good friend, Handler, recently confessed to knowing nothing about the wedding.

"I know she's engaged but that's all I know," Chelsea Handler told talk show host Katie Couric. "I'm sure I'll find out about it when it's about to happen ... for privacy issues."